The invention relates generally to grading or sizing and more particularly to vision-based grading of individual food items.
Food items that are individually processed without further subdivision, such as shrimps and chicken parts, often have to be sorted into grades by size or weight. Head-on, headless, and peeled shrimps, for example, are typically graded by weight using one of three methods:
A) by hand, where shrimps are placed into appropriate size-bins after their weights are visually approximated or individually weighed on a scale;
B) with checkweighers, such as weigh belts, where shrimps pass one at a time over a belt-covered scale before being conveyed through actuated gates into appropriate size-bins; or
C) with mechanical devices that sort the shrimps based on their width, such as roller-gap graders where, by virtue of diverging gaps between adjacent rollers, larger shrimps progress farther down the inclined rollers before falling through the gaps into sequential size-bins.
All these approaches have significant drawbacks. Approach A is extremely slow if shrimps are individually weighed and inaccurate if size is visually approximated. Approach B permits faster weighing of individual shrimps, but checkweigher accuracy suffers when individual shrimps are weighed, and throughput is limited because only one shrimp can be accommodated at a time. Approach C permits much higher throughput, but is relatively inaccurate because correlation of shrimp weight to roller gap is affected by multiple variables, some controllable, such as roller speeds and water flow rates, and some uncontrollable, such as shrimp shape, texture, and firmness.